1. Field of the Invention
The invention relates to a method and apparatus for high performance switching in local area communications networks. In particular, the invention relates to a process of accomplishing two read operations and two write operations during a clock cycle.
2. Description of the Related Art
A switching system may include one or more network devices, such as an Ethernet switching chip, each of which includes several modules that are used to process information that is transmitted through the device. Specifically, the device includes at least one ingress module, a Memory Management Unit (MMU) and at least one egress module. The ingress module includes switching functionality for determining to which destination port a packet should be directed. The MMU is used for storing packet information and performing resource checks. The egress module is used for performing packet modification and for transmitting the packet to at least one appropriate destination port. One of the ports on the device may be a CPU port that enables the device to send and receive information to and from external switching/routing control entities or CPUs. Some devices also include a CPU processing module through which the device interfaces with external CPU ports.
One aspect of a network device that can result in a bottleneck that can hamper overall processing speed of the network device is the reading and writing of data to a memory. The buffers that are contained at the output ports are not sufficient to hold all of the data that may be sent out. In addition, output ports may have different speeds and may need to receive more or less data depending on operating conditions. Therefore, the function of the MMU becomes very important, in that the unit assists in the flow of data and determines how quickly data can be written to and read out of a memory. Thus, there is a need in the prior art for enhanced methods of reading and writing data that will not adversely affect the throughput of a network device.